Single-lens 3D method, microscope, and video adapter

ABSTRACT

A method and teaching for creating stereographic images with the use of a single lens is presented. A leading linear polarizing filter, a passive half-wave retarder, an electric switched quarter-wave retarder, and a trailing linear polarizing filter are then used in various combination to create: a 3D microscope, a 3D video adapter for microscopes, a general purpose 3D video lens, a 3D video adapter, and a 3D light-valve. A neutral density filter replaces those components to then create a 3D ocular and a 3D ocular adapter.

BACKGROUND OF THE INVENTION

The present invention relates to a system for producing stereographicimages with a single lens. We show that this system can be extended to amicroscope, to microscope ocular adapters, to a stereographic videolens, and to a stereographic adapter for any video capable device.

Optical systems such as a microscope typically produce a two-dimensionalimage of the subject under view. In a microscope an intermediate imageis viewed through ocular eyepieces or is focused at an image plane whereit may be recorded with a video camera. The usual microscope contains asingle objective lens, which functions to produce a magnified image ofthe subject to be viewed, and either a single ocular for viewing with asingle eye, dual oculars for viewing with right and left eyes, or anaccess hole for recording magnified images with a still or video camera.Because the image is produced with a single objective lens, the viewerhas had no perception of depth.

Heretofore, proposals have been made in prior art for stereographicviewing with microscopes that use a single objective lens. All of themsuffer from problems and limitations.

Carter 1988, in U.S. Pat. No. 4,761,066, proposes orthogonally opposinglinear polarizing filters adjacent to the objective lens with left andright matching linear polarizing filters in the binocular oculars. Thismethod suffers from three problems. First, the position of theorthogonally opposing linear polarizing filters are adjacent to theobjective which prevents use with powers higher than 10×. Second, theuse of linear polarizing filters in the oculars causes alignmentproblems when the oculars rotate as when focusing. And Third, the use oflinear polarizing filters near the image plane causes distortion andvisual noise from contaminants.

Greenberg 1999, in U.S. Pat. No. 5,867,312, proposes a variation onSchulman 1941, in U.S. Pat. No. 2,255,631, wherein polarized or coloredlight from two or more axially differentiated paths is projected eitherdown through a single objective or up through the specimen to be viewed.The differently linearly polarized light is then viewed by theappropriate oculars thus producing a stereographic effect. This methodworks well at low magnifications, but produces reduced stereographicinformation as magnification increases. Because polarized light istransmitted through the subject, polarizing subjects can severelydistort the quality or perceptibility of the perceived image. Finallynote that Schulman suffers from many of the problems of dual-lens thatlead to viewer discomfort.

Tandler 1998, in U.S. Pat. No. 5,835,264, utilizes an approach thatparallels Greenberg 1999, wherein linearly polarized light is projectedeither down through a single objective or up through the specimen. Thisapproach shares the same limitations as Greenberg 1999.

Songer 1973, in U.S. Pat. No. 3,712,199, discloses a method forproducing stereoscopic motion pictures using only a single lens. Thatapproach utilized anaglyphic filters at the aperture stop, a techniquethat has been demonstrated to not work well with Video. Songer 1997, inU.S. Pat. No. 5,671,007, discloses a method for producing stereoscopicvideo using only a single lens. That approach requires an activeswitching occluding device, termed a “light-valve,” to be placed at theaperture stop of the lens. Use of an active element in a lens is morecostly to install, more difficult to maintain, and, when it fails,significantly degrades the optical properties of the lens. The method wedisclose herein places a passive system at the aperture stop of thelens. A passive system is less expensive to install, requires nomaintenance, and cannot fail. Because the passive component only effectsthe orientation of polarization, it is essentially invisible, and thusdoes not change the nature of the lens unless that lens is used inconjunction with external components to create a stereographic effect.Songer also advises using an off-the-shelf light-valve, withoutdisclosing the nature or construction of such a light valve. Suchcomponents typically use opposing polarization at the aperture stop,thus preventing them from being used to photograph the sky, water, orreflecting surfaces that effect polarization. The method we discloseherein uses a single polarizer ahead of the aperture stop, which allowsthose subjects to be successfully photographed.

Shipp in U.S. Pat. No. 5,471,237 discloses an active shutter mountedtransversely across the optical tube. No mention is made of where in thelight path such a shutter should be mounted. Like Songer above, Shippuses an active shutter inside the lens system which produces a similardisadvantageous failure mode.

Lia in U.S. Pat. No. 5,222,477 discloses two holes on either side of asingle lens. Lia confuses dual-lens with single lens technologies. His“left and right pupils” emulate the human-eye method (dual-lens) ofviewing. Lia also fails to specify that the “left and right pupils” mustbe placed at the aperture stop or one of its conjugates.

Greening in U.S. Pat. No. 5,828,487 discloses a switching device betweenthe lens system and the camera. Greening fails to specify that theopaque leaf must be positioned at the aperture stop or at one of theconjugates of the aperture stop. The use of a mechanical opaque shutterleads to a failure mode which causes the shutter to center and thus makethe entire system unusable.

Watts in U.S. Pat. No. 5,914,810 and GB2298989 places an active “opticalshutter” that “constitutes the iris” inside a lens. The active opticalshutter is the same as the active light-valve above specified by Songerfor motion pictures, but here used for an endoscope. This opticalshutter suffers from the same drawbacks as the light-valve of Songer.The specification of the iris fails to recognize that the aperture stopor any conjugate of the aperture stop are the preferred location for theoptical shutter.

SUMMARY OF THE INVENTION

It is therefore a general object of the invention to provide an opticalsystem which largely overcomes the above-mentioned problems andlimitations associated with prior art microscopes and video lenses.

A specific object of the invention is to disclose and claim theunderlying method of producing a stereoscopic effect with just a singlelens.

A specific object of the invention is to provide a stereo-microscopewhich is a significant improvement over Carter, 1988. One improvement isto replace the two polarizing filters at the oculars with a singlepolarizing beam splitter. Another improvement is to set the location ofthe filter to the aperture stop, or to one of the aperture stop'sconjugates.

A specific object of the invention is to provide a video camera adaptersuitable to produce stereo-microscopic images on any microscope thatuses a single objective lens. One implementation is to use an electricswitched quarter-wave retarder and a final linear polarizing filter inconjunction with a modified objective to produce a video image. Anotherimplementation is to use an adapter between the camera and an unmodifiedmicroscope to produce stereoscopic images.

A specific object of the invention is to provide an ocular and an ocularadapter, pairs of which can produce stereoscopic images when used inconjunction with any unaltered single objective binocular microscope.

A specific object of the invention is to provide a video lens system,which is a significant improvement over Songer 1997, capable ofproducing a stereoscopic effect when in conjunction with any standardvideo camera body, as on a microscope.

A specific object of the invention is to provide an adapter than canproduce a stereoscopic effect when used in conjunction with any standardimaging lens, such as a microscope's objective, and camera body.

A specific object of the invention is provide a stereographiclight-valve that can be used in or with any imaging lens, such as amicroscope objective, a video lens, or a motion picture lens.

These and other objects and features of the invention will become morefully apparent when the following detailed descriptions are read inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B show two views of foreground and background subjectpoints imaged on an image plane.

FIGS. 2A and 2B show two representations of lens systems and theposition of the aperture stop in each.

FIG. 3 shows that a lens system may have an aperture stop and manyconjugates of that aperture stop.

FIG. 4 shows that light travels parallel to the axis of the systemthrough the aperture stop.

FIG. 5 shows the result of an aerial image projected into a human eye.

FIG. 6 shows a hypothetical optical-encoding filter.

FIG. 7 shows the hypothetical optical-encoding filter interposed at theaperture stop of a lens system.

FIGS. 8A and 8B together illustrate that the filter must reside at theaperture stop, not near the aperture stop.

FIGS. 9A and 9B show two views of the out-of-focus area of a foregroundpoint when the hypothetical filter is used.

FIGS. 10A and 10B show two views of the out-of-focus area of abackground point when the hypothetical filter is used.

FIGS. 11A and 11B show the combined effect of the hypotheticaloptical-encoding filter on the foreground and background out-of-focusregions.

FIGS. 12A, 12B, and 12C show three actualizations derived from thehypothetical optical-encoding filter and their effect on the foregroundand background out-of-focus areas.

FIGS. 13A, 13B, and 13C show the effect of the three actualizations onthe human eye.

FIGS. 14A, 14B, 14C, 14D, and 14E show variations on the division of theoptical-encoding filter.

FIG. 15 shows the slope associated with the out-of-focus areas.

FIGS. 16A and 16B show the difference between dual-lens 3D andsingle-lens 3D and illustrates two advantages that single-lens 3D hasover dual-lens 3D.

FIGS. 17A and 17B show the polarizing effect of the existing“light-valves.”

FIG. 18 shows our implementation with a passive component at theaperture stop.

FIGS. 19A, 19B, and 19C show the three polarizing orientating effectsproduced by the electric switched quarter-wave retarder.

FIGS. 20A, 20B, and 20C show the output polarizing effects of the threepolarizing orientating effects produced by the electric switchedquarter-wave retarder.

FIGS. 21A, 21B, 21C, and 21D show the cut edge that needs treatment, thecoating on glass, and a glass sandwich of the optical-encoding filter,and a glass sandwich of the optical-encoding filter and the leadinglinear polarizing filter.

FIG. 22 shows the relationship of the four components: a leading linearpolarizing filter, a passive half-wave retarder, a electric switchedquarter-wave retarder, and a trailing linear polarizing filter.

FIG. 23 shows a converter that converts a video signal to toggled energyfor the electric switched quarter-wave retarder.

FIG. 24 shows the important components of a binocular microscope'soptical path with a modified objective and a polarizing beam splitter asindicated.

FIG. 25 shows alternate positions for the leading linear polarizingfilter.

FIG. 26 shows a video camera adapter in conjunction with the use of amodified objective lens.

FIG. 27 shows a video camera adapter with alternative positions for theelectric switched quarter-wave retarder.

FIG. 28 shows the Carter 1988 method of modifying a microscope objective(prior art).

FIG. 29 shows the diagrammatic view of a video adapter that allowsstereographic imaging with any unmodified microscope.

FIG. 30 shows the result of the second embodiment.

FIG. 31 shows how half occluded relay lens systems in front of theoculars of a binocular microscope can achieve the same effect as FIG.30.

FIG. 32 shows the diagramic view of an ocular, pairs of which allow anymicroscope to produce stereographic images.

FIG. 33 shows the diagrammatic view of an adapter, pairs of which allowany ocular to produce stereographic images on any microscope.

FIG. 34 shows variations on the shape of the neutral density filter andholes that are used to occlude the ocular and the ocular adapter.

FIG. 35 shows variations on the transmission density of the neutraldensity filter used to occlude the ocular and ocular adapter.

FIGS. 36A and 36B show treatment of the refracting edge of the neutraldensity filter used in the ocular and ocular adapter.

FIG. 37 shows a video lens capable of producing a sequence ofstereographic pairs of images.

FIG. 38 shows an aperture stop that is outside the video lens system.

FIGS. 39A and 39B show alternative positions for the leading linearpolarizing filter.

FIGS. 40A, 40B, 40C, and 40D show alternative positions for the electricswitched quarter-wave retarder.

FIG. 41 shows that the electric switched quarter-wave retarder may beinside the camera body.

FIGS. 42A and 42B show alternative positions for the final linearpolarizing filter.

FIG. 43 shows a diagrammatic depiction of the video adapter.

FIG. 44 shows an exploded view of the video adapter.

FIG. 45 shows the components that make up the light-valve.

FIG. 46 shows an exploded view of the light-valve.

FIG. 47 shows that the passive half-wave retarder can be applied as acoating to a glass disk.

DETAILED DESCRIPTION OF THE INVENTION

A. The Means of Encoding

The first embodiment is a means for distinguishing foreground frombackground information in a single lens system. This system differs fromtraditional means of detecting and displaying depth information thatrely on two or more lenses to create parallactic views. Instead ofrelying on parallactic displacement to determine the depth and positionsof objects, this single-lens system utilizes information encoded intothe out-of-focus areas of the image. This embodiment deals with themethod for encoding that depth information into the out-of-focus areas,and defers any claim to viewing and interpreting that depth informationto standard stereographic techniques.

Among all single lensing systems are two general classes of lensingsystems used to produce images. The first form is any lensing systemcapable of projecting a subject as an image of that subject onto animage plane. One example of such an implementation of this approach isthe lens of a video camera. The second form is any lensing systemcapable of projecting a subject as an aerial image suitable for directviewing by a human eye (where the retina of the eye is another imageplane). One implementation of this approach is a microscope ocular. Forthe purposes of preliminary discussion, the two forms will be consideredidentical, and we describe them showing only the first. This reductionin the scope of the discussion is not, however, intended to be limitingbecause both approaches project a subject as an image of that subjectonto an image plane.

FIG. 1A shows three points, 4, 6 and 9, relative to the subject planerepresented by the dashed line 2. A lens 1 gathers light from point 4 onthe subject plane 2 and projects an image of that point onto the imageplane 3, indicated by the dashed line, at position 5. The image point atposition 5 is in-focus because it is positioned precisely at the imageplane.

Point 9 lies behind the subject plane 2 (further from the lens 1 than isthe subject plane) and is thus a background point. When a backgroundpoint is projected onto the image plane, as point 9 is projected toimage position 10, it is focused at a point in front of the image plane3 (nearer to the lens than is the image plane). The area, as at region11, where the light that forms the image for point position 10intersects the image plane, is an out-of-focus image of point 9, thebackground point. An out-of-focus image of a point is also called thecircle of confusion.

Point 6 lies in front of the subject plane 2 (closer to the lens 1 thanis the subject plane) and is thus a foreground point. When a foregroundpoint is projected onto the image plane, as point 6 is projected toimage position 7, it is focused at a point in back of the image plane 3(further from the lens than is the image plane). The area, as at region8, where the light that forms the image for point position 7 intersectsthe image plane, is an out-of-focus image of point 6, the foregroundpoint. That out-of-focus region is also called the circle of confusion.

FIG. 1B shows the image plane 3 of FIG. 1A rotated 90° so that its backfaces outward from the page. This back view of the image plane 3 showsthe image of the in-focus point at location 5. The circle of confusionfor the foreground out-of-focus point is shown at the top location 8,and the circle of confusion for the background out-of-focus point isshown at the bottom location 11.

The circles of confusion are visually identical for region 8 (createdfrom the background point) and region 11 (created from the foregroundpoint). When both points are of equal color and intensity, and when bothproduce equal size regions, it is not possible to distinguish one fromthe other, that is, it is not possible to distinguish background fromforeground information.

FIG. 2A shows one common implementation of an imaging lens system 12. Init, the position of its aperture stop is indicated by the dashed line at13. The aperture stop is that position within a lensing system whereoptical control elements may be placed without being imaged. One suchcommon control element is an iris for altering the amount of lightpassing through the lens system. Note that the iris is sometimesreferred to as the aperture, and that this use of the term aperture isdistinct from the term “aperture” stop we use herein. FIG. 2B shows adiagrammatic representation of a lensing system 12 used forillustration. In it, the location of the aperture stop is indicated bythe dashed line 13.

FIG. 3 shows that some lensing systems can have multiple aperture stops.In general, the aperture stop inside the lens system 14 nearest thesubject plane 2, is called the aperture stop of the lens system. In FIG.3, the aperture stop of the lens system is indicated by the dashed line13. Other aperture stops, called conjugates of the aperture stop, cancoexist in a lens system as shown in FIG. 3 by the dashed line 15. Whena new aperture stop is created in front of or behind the lens system,they too are called conjugates of the aperture stop. The conjugate infront of the lens system is indicated by the dashed line 16. Theconjugate behind the lens system is indicated by the dashed line 17. Anyconjugate of the aperture stop is included in this embodiment. Thebehavior of the encoding is unaffected by whether or not the actualaperture stop is used, or if one of the conjugates of the aperture stopis used, or if the encoding method to be disclosed is placed in anycombination of the aperture stop or any of its conjugates.

FIG. 4 shows the simplified diagram of a lens system 12. The aperturestop, indicated by dashed line 13, is a plane perpendicular to theprincipal ray (the main axis of light) 18 through the lens system. Thesubject point 4 rests on the subject plane, indicated by the dashed line2. Light rays from point 4 are indicated by lines 22. Those light raysexpand from point 4 on the subject plane 2, are brought into parallel bythe leading lens element 19 of the lens system, and then are focused onthe image plane 3 by the final lens element 20 of the lens system.Region 21 is the gap between the lens system elements where light runsparallel to the principal ray (the main axis of light) 18 through thelens system. The aperture stop of this system is indicated by dashedline 13, and is the plane through which the light first starts to travelparallel to the main axis of the system.

FIG. 5 shows part of a lensing system 14, the rear element 20 of whichis designed to produce an aerial image, as represented by the lines 22representing light paths. An aerial image is one in which the lighttravels parallel (as if focused on infinity), and is an image suitablefor direct viewing by the human eye. The human eye 23 perceives theparallel light produced by the aerial image and focuses it on the retinaof the eye (not shown). The plane where the parallel light first exitsthe lens system 14 is another conjugate of the aperture stop. Thisparticular conjugate has the special name “exit pupil” and is shown bythe dashed line 25. The plane of parallel light that is lastly parallelbefore being focused on the retina has the special name “entrancepupil.” That plane, the iris of the eye 24, is another conjugate of theaperture stop. Lenses in addition to the human eye also have entrancepupils. A camera lens, for example, also images parallel light at itsfront lens element, thus creating an entrance pupil. For the purposes ofthis embodiment, the entrance pupil and exit pupil are also consideredusable conjugates of the aperture stop.

The subject invention manipulates the image or part of the image toencode the image with depth information. FIG. 6 shows the front view ofan optical-encoding filter 26, the left half 27 of which changes lightin manner X and the right half 28 of which changes light in the mannerY. For example, one implementation is an X that is a red filter, and a Ythat is a cyan filter. Another implementation is an X that is horizontalpolarization and a Y that is vertical polarization. The implementationthat yields a difference between X and Y is unimportant to thisembodiment at this point in the disclosure. The important point is thatX and Y differ in how they effect the light. This manipulation of thelight creates two different image signals.

FIG. 7 shows a lensing system 12 into which the optical-encoding filter26, of FIG. 6, has been placed at the aperture stop indicated by dashedline 13. The placement of the optical-encoding filter at the aperturestop is critical. The aperture stop, or one of its conjugates, is theone place in the light path where the optical-encoding filter will onlyeffect the quality of light, and will not produce an image of itself.Near the aperture stop will not work. FIGS. 8A and 8B showdiagrammatically why the optical-encoding filter must be at the aperturestop. If the optical-encoding filter is an occlusion that blocks halfthe aperture stop, as at 29 in FIG. 8A, it reduces the total lightpassed through the lens system by 50%, or one stop and in no other wayeffects the image. If that occlusion is moved from the aperture stop, asat 29 in FIG. 8B, the effect is much different. If, for example, it islocated a distance that is equal to the lens diameter away from theaperture stop, on an f/2 lens, the effective lens speed reducesdramatically. For light entering the lens 27° off-axis the effectivespeed of the lens reduces to f/5. For light entering the lens 45°off-axis the effective speed of the lens reduces to f/10000, effectivelyzero transmission of light. The visual effect of an image produced bysuch a lens is one of a vignetted picture, or of tunnel vision. Thefurther the filter is from the aperture stop, the more pronounced thisaberration becomes. Actual experience shows visually perceptiblevignetting when, on an f/2, 50 mm lens, the occlusion is only 2 mm fromthe aperture stop.

FIG. 9A shows the effect of a properly placed optical-encoding filter 26when a foreground point 6 is projected through it. The foreground point6 focuses to point 7 behind the image plane 3, thereby creating thecircle of confusion (out-of-focus area) at 8 on the image plane. FIG. 9Bshows the same image plane 3 rotated so that its back side may be fullyviewed. The circle of confusion 8 takes on the characteristics of theoptical-encoding filter 26. That is, for example, if X is red, and Ycyan, those colors would appear in the identical regions of the circleof confusion 8, with red to the left and cyan to the right.

FIG. 10A shows the effect of a properly placed optical-encoding filter26 when a background point 9 is projected through it. The backgroundpoint focuses to point 10 in front of the image plane 3, then continues,crossing through itself, striking the image plane and thereby creatingthe circle of confusion (out-of-focus area) 11 in the image plane 3.FIG. 9B shows the same image plane 3 rotated so that its back side maybe fully viewed. The circle of confusion 11 takes on the inversecharacteristics of the filter 26. Because the circle of confusion isreversed and inverted, the characteristics of the filter are alsoreversed and inverted from those at 8 in FIG. 9B.

The introduction of a manipulation means such as a specially composedoptical-encoding filter at the aperture stop of an imaging lensingsystem has caused foreground and background circles of confusion todiffer in a readily detectable manner when projected onto the imageplane. This difference can produce a 3D effect when viewed by humans andcan yield depth data for use to automated processes.

FIGS. 11A and 11B show the combined effect of the optical-encodingfilter 26 at the aperture stop represented by the dashed line 13 in thelens system 12. FIG. 11A shows that the background point 9 is focused toa point in front of the image plane at 10. Where the light for imagepoint 10 continues to the image plane, an out-of-focus area is createdat 11. FIG. 11B shows that the out-of-focus area for the backgroundpoint 11 takes on the inverse characteristics of the optical-encodingfilter 26. FIG. 11A also shows that the foreground point 6 is focused toa point in back of the image plane at 7. Where image point 7 passesthrough the image plane an out-of-focus area is created at 8. FIG. 11Bshows that the out-of-focus area for the foreground point 8 takes on thecharacteristics of the optical-encoding filter 26. FIG. 11A also showsthat any point on the subject plane 4 is focused onto a point on theimage plane 5. All points on the subject plane 2 will always be in-focuson the image plane 3. When this system produces a union of foregroundand background information (as when 3D is viewed in 2D without specialequipment) the result is an unambiguous image that can be viewed in 2Dcomfortably.

FIGS. 12A, 12B, and 12C show four image planes 3, each showing theresult of an optical-encoding filter used to differentiate backgroundfrom foreground circles of confusion. FIG. 12A shows the result of anoptical-encoding filter that uses vertical polarization to the right andhorizontal polarization to the left (recall that the view is from theback side of the image plane 3). The foreground circle of confusion 8 ispolarized in the same pattern as was the filter. The background circleof confusion 11 is polarized in the reverse pattern. FIG. 12B shows theresult of an optical-encoding filter that has red to the right and cyanto the left. The foreground circle of confusion 8 shows the samered/cyan ordering as did the filter. The background circle of confusion11 shows the reverse pattern.

FIG. 12C shows the result of another type of manipulation by asequential filter. In such a filter, first a portion such as half of theaperture stop is covered and the resulting image stored. Then the secondportion or half of the aperture stop is covered and the first isuncovered, and the resulting image stored. FIG. 12C shows the differencebetween background circles of confusion 11 and foreground circles ofconfusion 8 as two discretely different image planes 3 are produced overa time interval.

Humans are able to derive a 3D effect from any of these optical-encodingimplementations. All that is needed is for one eye to only see thehalf-circles of confusion produced by half the optical-encoding filter,and for the other eye to see the half-circles of confusion produced bythe other half of the optical-encoding filter. Both eyes are able to seeall the information from both halves when that information is in-focusat the image plane.

FIGS. 13A, 13B, and 13C show what each eye sees when each is coveredwith an appropriate complimentary material. FIG. 13A, for example, showswhat each eye sees when one is covered with vertical polarizing materialand the other with horizontal polarizing material. FIG. 13B shows whateach eye sees when one is covered with a red filter and the other iscovered with a cyan filter. And FIG. 13C shows what each eye sees whenone is covered with opaque material when viewing the first of a sequenceof images, and the other eye is covered with opaque material whenviewing the second of a sequence of images. Naturally such a sequence ispresented sufficiently rapidly for persistence of vision to have effect.

Finally note that the optical-encoding filter does not have to be abifurcated circle. There is advantage to optical-encoding only the sidesand leaving the middle clear, as in FIG. 14A, where the clear verticalstrip up the middle increases vertical resolution of the system whilereducing the perceived 3D effect. FIG. 14C shows that theoptical-encoding can divide the aperture stop into more than just twopieces. Three pieces can encode a vertical component, thereby providingvertical as well as horizontal head-motion parallax when viewing. FIG.14C shows that the aperture stop can be encoded in novel ways, thisparticular example being more suitable to machine interpretation thanfor human viewing. FIG. 14D shows that the optical-encoding can berotated to a horizontal position to turn off the human perceived 3Deffect, as when 3D is confusing during a medical procedure. FIG. 14Eshows that the optical-encoding components can overlap. This causeshigher light loss but that detriment can be overcome by making thecomponents translucent or neutral density.

B. The Theories

There are two theories why this method can produce images that can beviewed by humans in a manner that is clearly perceptible as astereographic experience. Neither, as of this writing, has been proven,but they are included here for completeness of disclosure.

One theory holds that the brain can meld the two out-of-focus areasbecause they have the property of “self-similarity.” That is, thebilateral symmetry of the optical-encoding allows the brain to “glue”the two generated sides of information back together, thus recognizingthat foreground differs from background. This theory implies that thetwo parts of the optical-encoding at the aperture stop must bebilaterally symmetric, and that non-symmetric encoders will fail toproduce a stereographic image, a supposition that has not yet beentested.

Another theory holds that the bilateral nature of this effect gives thebrain the effect of a slope which suggests depth relationships. FIG. 15shows how the sizes of the out-of-focus areas in the image plane vary asthe subject points increase distance from the subject plane as indicatedby the dashed line 2. Leftmost dashed line 30 shows the slope of thosesizes as viewed from the left eye. Rightmost dashed line 30 shows theslope of those sizes as viewed from the right eye. The two slopesconverge in the distance (the background) much as two perspective lineswould converge. This theory implies that the two parts of theoptical-encoding at the aperture stop must occupy the same width, butneed not otherwise be symmetric, a supposition that has not yet beentested.

C. Competing Methods

The method of this embodiment differs markedly from the traditionalunderstandings of how 3D effects are produced. The most common approachto producing 3D is by use of two lenses in a parallactic displacementarrangement. FIG. 16A shows this dual-lens approach. In it, the subject31 is viewed independently by two lensing systems. The left view of thesubject is captured by the leftmost lensing system 1 whereafter thatview is projected onto the leftmost of two image planes 3. The rightview of the subject is captured by the rightmost lensing system 1,whereafter that view is projected onto the rightmost of the two imageplanes 3. Each image plane holds a totally separate view of the object,one shifted left of center and the other shifted right of center.

FIG. 16B shows this embodiment and teaching as disclosed herein. In it,the subject 31 is viewed by a single lens into the aperture stop ofwhich has been inserted the optical-encoding filter 26. A beam splitter34 causes identical images to be sent to the left and right. The filter33 eliminates from the common image all circle of confusion informationexcept that allowed to pass by filter side Y. The filter 32 eliminatesfrom the common image all circle of confusion information except thatallowed to pass by filter side X. Both side filters allow identicalin-focus information to pass. The leftmost of the image planes 3receives an image, the in-focus part of which is identical to thein-focus part of the image received by the rightmost of the image planes3. The only information that differs between the two image planes is thecircle of confusion (out-of-focus) information that carries the encodeddepth or 3D information.

Visually, this single-lens 3D embodiment is very different fromdual-lens 3D. Single-lens 3D suffers from no parallactic displacement.With dual-lens 3D, parallactic displacement 36 often leads tokeystoning, double image distortions, cross talk and ambiguous borderinformation. Also single-lens 3D retains a full core of information,whereas dual-lens 3D can miss critical core information, as at 35 (forexample, cannot look down holes).

With dual-lens 3D images can appear in-focus in front of the image planeor behind it. When the human eye attempts to focus on an object thatdoes not exist in actual space, eye strain and fatigue can ensue. Withsingle-lens 3D no in-focus part of the image can ever exist out of theimage plane. The human eye is naturally drawn to focus on the imageplane where is should be focused.

Another competing method is the Schulman approach first disclosed inU.S. Pat. No. 2,225,631. Schulman noted that a stereovision effect couldbe achieved by lighting a subject from two sides. Arrangement is made ismade so that one eye sees only the image lit from a corresponding side,and the other eye sees only the image lit from the other correspondingside. This effect can produce good stereoscopic views. When used inmicroscopes, the stereoscopic effect is reduced as magnificationincreases. At macro levels this method is difficult because of thecomplexity of deploying large displaced lights. Although Schulman uses asingle lens, it nevertheless suffers from many of the flaws of dual-lensthat lead to viewer discomfort, such as, causing the eye to focusoutside the image plane, and distinctly different images being presentedto each eye.

Other methods exist that are variations on these two other approaches.

D. The Invention

Our implementations only require use of a passive element ormanipulative means at the aperture stop of the lens system. Thisapproach has several advantages over the other approaches. The typicalstereographic “light-valve” is composed of two opposing linearpolarizing filters as shown in FIG. 17A. The vertical orientationindicator 45 shows that the left side of the aperture stop is coveredwith polarizing material that polarizes in the vertical orientation. Thehorizontal orientation indicator 46 shows that the right side of theaperture stop is covered with polarizing material that polarizes in thehorizontal orientation.

FIG. 17B shows a sequence of effects on the aperture stop caused by thecommon form of “light-valve” that is composed of two half FeroElectricLiquid Crystal (FLC or FELC) switches. Such switches operate each halfalternately, one occluding and the other allowing light through, thenthe second occluding and the first allowing light through the firsthalf. The light passing parts are typically oriented in opposingpolarizing orientations.

When opposing sides of the aperture stop are orthogonally polarized, aninteresting effect is imposed on the viewer of the resulting images.Sky, water, and other reflecting and polarizing effecting surfaces willappear different to each eye. Sky, for example, will appear very dark toone eye and will appear very light to the other eye. This can appear tostrobe in video and film presentations, and lead to eyestrain when usedwith still image presentations.

Our implementations are quite different and produce a much more pleasingeffect. As shown in FIG. 18, non-polarized light enters the light pathat 47. A leading conditioner such as a linear polarizing filter 40polarizes all light entering the system in the same orientation as shownby indicator 45. Whatever polarizing orientation outside subjects mayhave had, such as sky, will be polarized once and uniformly. If the skyis dark, for example, it will remain dark thereafter. A passivehalf-wave retarder 38 is placed at the aperture stop and cut so that itonly occupies a portion such as one half of the aperture stop. Acorrectly oriented passive half-wave retarder will shift the polarizingorientation of the light passing through it by 90° and thus manipulatethe image signal of that portion of the light. The result on the lightpath is a left side orientation that is vertical as at 45, and a rightside that is horizontal as at 46. But note that the polarizing orconditioning effect on the sky was done once by the leading linearpolarizing filter 40, and remains the effect thereafter. The change inone half the aperture by the passive half-wave retarder only effect thepolarizing orientation of the light, not the image that is being passedthrough it. Our implementation can be used with sky, water, and otherreflecting and polarizing altering materials with no conflict betweenwhat each eye sees. It does not strobe when used with video and movies,and produces no eyestrain.

Another advantage of our implementation is that we place a passivecomponent at the aperture stop of the lens system. The passive half-waveretarder 38, once installed, requires no maintenance and no adjustmentover time. Because it is passive, unlike existing commercial“light-valves,” it is neither prone to failure nor prone to need forperiodic replacement. That the passive half-wave retarder is placed atthe aperture stop of the lens system is not intended to be limiting,however, as it is well known that lens systems may have multipleaperture stops, called the aperture stop and its conjugates. Suchpositionings of the aperture stop may nevertheless be employed in theinvention and those skilled in the optic arts will readily be able toextend the present principle to any conjugate of the aperture stop.

In addition to the passive element that is at the aperture stop, we alsouse a switched means to manipulate the light such as an electricswitched quarter-wave retarder (optical switches or magnetic switchesare also possibilities) which can be anywhere in the light path betweenthe leading and trailing linear polarizing filters, but which isgenerally not placed at the aperture stop. FIG. 19A shows an electricswitched quarter-wave retarder 48 that is powered by wires 49. In itsnon-powered state its effect on polarizing orientation is neutral,rotating that orientation only 45°. This allows light to pass throughboth sides of the aperture. Unlike failure modes of earlier art, oursystem fails in a way that allows a full image to pass, but only loses3D information. Such a failure mode is critical in such fields asmedicine and other life-critical missions. FIG. 19B shows the effectwhen the electric switched quarter-wave retarder is powered one way 50.It rotates the polarization orientation of light to one polarizingorientation. When it is powered in the other direction, as at 51 in FIG.19C, it rotates the polarization orientation of light to the otherpolarizing orientation.

FIGS. 20A, 20B, and 20C show the effect of the three polarizingorientating directions of the electric switched quarter-wave retarderwhen combined with a trailing linear polarizing filter 41 (also calledan analyzing polarizer). FIG. 20A shows that when the electric switchedquarter-wave retarder is in its neutral orientation 48 the polarizationorientation of the two halves of the aperture stop are rotated 45°, thusallowing both sides to pass through the trailing linear polarizingfilter 41. FIG. 20B shows that when the electric switched quarter-waveretarder is powered into its counter clockwise direction 50, thepolarization orientation of the two halves of the aperture stop arerotated 90° thus allowing only the light from the passive half-waveretarder 38 side of the aperture stop to pass through the trailinglinear polarizing filter. FIG. 20C shows that when the electric switchedquarter-wave retarder is powered into its clockwise direction 51, thepolarization orientation of the two halves of the aperture stop are leftin their original orientation, thus allowing only the light from theunoccupied side of the aperture stop to pass through the trailing linearpolarizing filter.

Because only the passive half-wave retarder 38 needs to be in theaperture stop, the other components can be installed outside the lenssystem. Such an arrangement leaves a lens system that acts as thought itis unmodified unless combined with the other components. Thisarrangement has the advantage of allowing the creation of lenses thatcan be used for work other than 3D image production, a concern that manyusers will have when faced with a choice between single-use andmultiple-use expensive lenses.

E. Common Considerations

Our implementations share several common elements that we describe inone place here for simplicity.

As shown in FIG. 21A, the bisecting edge 39 of the passive half-waveretarder 38 may be treated to minimize unwanted refractive visual noise.One implementation is to coat the bisecting edge with light-absorbtivematerial, such as flat-black paint, dye, or a light absorbtive agent.Another implementation, as shown in FIG. 21B, is to apply the passivehalf-wave retarder as a coating 52 to an optically flat transparentsurface 53, such as glass. Another implementation, as shown in FIG. 21C,is to sandwich the passive half-wave retarder 38 along with transparentfiller material 78 between two optically flat transparent surfaces 53,such as glass. FIG. 21D shows that the leading linear polarizing filtercan be included in a sandwich with the components of FIG. 21C, where theleading linear polarizing filter must always precede the passivehalf-wave retarder in the light path. These implementations are notintended to be limiting, however, as it is well known that edgerefractions can be eliminated using any of a wide variety of methods.Any such method may nevertheless be employed in the invention and thoseskilled in the optic arts will readily be able to extend this principleto any method for eliminating undesirable edge refraction.

An electric switched quarter-wave retarder is any of a class of switchmanipulation means or devices that can change the orientation oflinearly polarized light by 45° in one direction when electricallyenergized and that can change the orientation of linearly polarizedlight 45° in the opposite direction when electrically energizedoppositely. One common implementation of an electric switchedquarter-wave retarder is as part of a FeroElectric Liquid Crystal switch(FLC or FELC), a device that can alter the orientation of linearlypolarized light by variable amounts in either direction under electricpotential control. Use of an FLC or FELC switch is, however, notintended to be limiting, as it is well known that linearly polarizedlight can be reoriented or manipulated by 45° in alternating directionsby many means, electric, optical, magnetic or mechanical. Any suchimplementation may nevertheless be employed in the invention and thoseskilled in the optic arts will readily be able to extend this principleto any method for reorienting linearly polarized light by 45° first inone, and then the opposite direction, under electric control. Thespecification of alternate 45° rotation is also not intended to belimiting because an electric switched quarter-wave retarder is variablein its rotation. Any degree of rotation that sums to a totalpolarization orientation change of 90° is acceptable, and any suchalternate divisions of rotation are a part of this embodiment.

In FIG. 22, the orientation of the electric switched quarter-waveretarder 48 parallels that of the leading linear polarizing filter 40.The two parallel each other when the electric switched quarter-waveretarder is in one or the other of its electrically energizedorientations but not both.

The polarization orientation of the passive half-wave retarder 38parallels that of the polarization orientation of the leading linearpolarizing filter 40. Current producers of passive half-wave retardermaterial mark the grain or neutral orientation of the material with anarrow or other indicator at the edge of the material. The material mustbe rotated 45° in either direction relative to its neutral orientationto bring its active polarization orientation into parallel alignmentwith the leading linear polarizing filter.

The electric switched quarter-wave retarder 48 is electrically energizedto set it into one or the other of its polarizing effectingorientations. The electric switched quarter-wave retarder is providedits energy via the wires 49. The energy supplied to the electricswitched quarter-wave retarder toggles it from one quarter waveorientation setting to the other and back again. As shown in FIG. 23, asignal originates at 56 inside the camera 55 and is passed to aconverter box 58 over the wires 57. The converter box converts theinternal signal produced by the camera into a form usable by theelectric switched quarter-wave retarder. The converted signal is passedfrom the converter box 58 to the electric switched quarter-wave retarder48 via wires 49. The converter can convert a standard analog or digitalvideo signal into a square wave for use by the electric switchedquarter-wave retarder. The conversion from analog or digital to a squarewave is intended to be illustrative of the general principle and is notintended to be limiting. Any method to drive the electric switchedquarter-wave retarder may nevertheless be employed in the invention, andthose skilled in the electric arts will readily be able to extend thepresent principles to an appropriate conversion circuit.

F. Stereographic Microscope

The second embodiment is a microscope with a single objective lens thatproduces a stereoscopic image when viewed through two oculars. Thisembodiment is a significant improvement over Carter 1988, which requiredseparate polarizing filters for each ocular and required the polarizingfilters to be adjacent to the objective lens.

In this embodiment, as shown in FIG. 24, the separate polarizing filtersof Carter 1988 are replaced by a single polarizing beam splitter 34 inthe binocular head of the microscope. The separate polarizing filters ofCarter 1988 tended to be placed too near the image plane of each ocular,subjecting them to dirt and other contaminants which reduced the qualityof the viewed image. Polarizing filters also tended to be placed on theoculars, thus preventing useful rotation of the oculars (as forfocusing), and caused them to easily fall out of alignment. Use of apolarizing beam splitter significantly simplifies manufacture andeliminates the problems associated with the earlier system.

In this embodiment, the opposing polarizing filters adjacent to theobjective (Carter 1988, as in FIG. 28) are replaced, in FIG. 24, with apassive half-wave retarder 38 at the aperture stop of the objective, anda single linear polarizing filter 40 anywhere in the light path prior tothat passive half-wave retarder. With Carter 1988 the filter was placedadjacent to the objective. Practical experience showed that such aposition only yielded acceptable stereopsis at powers of 10× and lower.By moving the filter to the aperture stop, or to any of the aperturestop's conjugates, all powers are made to produce good stereopsis.

The dashed line at 37 in FIG. 24 shows the vertical plane that dividesthe lens into two equal plane-symmetric halves. The passive half-waveretarder 38 covers one-half the area of the aperture stop with thebisecting edge 39 oriented perpendicular to plane 37 of the system. Thisorientation is not intended to be limiting, however, as it is well knownthat the ocular head can be rotated to accommodate different users, andthe orientation of the passive half-wave retarder is rotated in suchcircumstances to align with the polarizing beam splitter, inside therotated head.

As shown in FIG. 24, a leading linear polarizing filter 40 is interposedbetween the subject, a specimen normally held between the slide parts42, and the passive half-wave retarder 38. The ideal position is at theaperture stop, in the light path prior to, and immediately adjacent to,the passive half-wave retarder. Other positions are, as shown in FIG.25, a coating on the front element of the lens system 67, or as apolarizing slide cover 43. When the leading linear polarizing filter isin the light path prior to the subject, the subject becomes back-lit aswith a polarizing slide 44 or a polarized filtered illumination 40. Anyposition for the leading linear polarizing filter may be employed in theinvention so long as the leading linear polarizing filter is in thelight path prior to the passive half-wave retarder 38, and those skilledin the optic arts will readily be able to extend this principle to anyacceptable position inside or outside of the lens system.

G. Stereographic Video Adapters for Microscopes

The third embodiment, as shown in FIG. 26, is a video adapter capable ofproducing a stereoscopic image when used in conjunction with, andsubsequent in the light path to, a properly converted objective lens ona microscope. Included in this embodiment is an adapter that allows anyvideo camera to produced a stereoscopic image in conjunction with anyunconverted single-objective microscope. The video camera is digital oranalog.

In FIG. 4, the camera extension tube of a trinocular microscope isreplaced with the video adapter 54. That the camera extension tube isreplaced is not, however, intended to be limiting, because it is wellknown that images can be captured through the ocular holes as well. Byscaling the video adapter down to the correct diameter, it can also beused to replace the ocular of a monocular or binocular microscope. Infact, as video cameras become smaller over time, the tendency will be tomake the replacement of an ocular the preferred implementation.

The extension tube replacement 54 is normally threaded at its back witha C-mount (not shown in FIG. 26) so that any standard video camera body55 can be attached to it. Normally still-cameras mount with T-mountthreads and video cameras with C-mount threads. Such threading is not,however intended to be limiting, because it is well known that camerascan mount in a wide variety of manners. Nikon and Canon, for example,have proprietary mounts that normally need to be adapted to a T-mountscheme. Any required mount may be nevertheless be used in the invention,and those skilled in the mechanical arts will be readily able to extendthe present principle to the formulation of an appropriate mount.

The adapter tube 54 contains two optical elements, a final linearpolarizing filter 41 (also called an analyzing polarizer), and anelectric switched quarter-wave retarder 48. That these two elements arein the adapter tube is not, however, intended to be limiting. Either orboth may equally well be placed inside the camera body 55, atop theobjective 14, or in the objective 14. The preferred implementation is aspart of the adapter tube because this implementation allows manydifferent models and brands of video cameras to be used without the needto modify each. Nevertheless, one or both of the optical elements can beused inside the camera body and will still be considered part of thisembodiment.

As shown in FIG. 26, an electric switched quarter-wave retarder 48 isplaced anywhere between the leading linear polarizing filter 40 and thefinal linear polarizing filter 41. Position 48 is the preferredimplementation. In FIG. 27 we illustrate that the electric switchedquarter-wave retarder will work equally well in the light path prior tothe slide assembly 42 and in the light path subsequent to the leadinglinear polarizing filter 40, where the leading linear polarizing filteris itself in the light path prior to the slide assembly 42. The positionof the electric switched quarter-wave retarder is irrespective of theposition of the passive half-wave retarder (not shown in FIG. 27) insidethe objective 14. As shown, the electric switched quarter-wave retarder48 can be in the light path prior to the microscope slide 42 when theleading linear polarizing filter 40 is also in the light path prior tothe microscope slide.

As shown in FIG. 26, the final linear polarizing filter 41 is placedanywhere in the light path between the passive half-wave retarder 38 andthe image plane 3. The preferred implementation is inside the adaptertube 54 and in proximity to the electric switched quarter-wave retarder48, because this placement allows the adapter to be used with a varietyof video cameras. As mentioned, the final linear polarizing filter canalso be located inside the camera body.

The final linear polarizing filter 41 has its polarization orientationoriented in parallel with the polarization orientation of the leadinglinear polarizing filter 40.

As shown in FIG. 26, the normal upright orientation of the camera, asindicated by 45, parallels that of the edge cut of the passive half-waveretarder 38.

The adapter of FIG. 26 may also be used with an objective lens that hasbeen modified with a modest variation on the Carter 1988 method. FIG. 28shows such an objective lens 14. When the adapter is used with such alens, the positioning rules are the same as if the left 59 and right 60linear polarizing filters are viewed as a combined linear polarizingfilter and passive half-wave retarder.

All the optical elements that combine to produce the stereoscopic streamcan be combined into a single adapter. When they are so combined, theresult is an adapter that will work with any unmodified non-3Dmicroscope. FIG. 29 shows diagrammatically such a collapsing of elementsinto a single adapter.

As shown in FIG. 29, a relay lens system bracketed at 77 is required toproduce a conjugate of the original aperture stop as indicated by thedashed line 15. The passive half-wave retarder 38 is placed at thecreated conjugate of the aperture stop. The relay lens system 77 takesthe incoming image, the light path of which is indicated by 22 thatoriginally focused on the image plane represented by the dashed line 3,and re-projects that image onto a new image plane represented by thedashed line 79.

The relay lens system, shown bracketed by 77, is depicted with simplelenses for the purpose of illustration. In actual practice, such relaylens systems are composed of compound lenses that are achromatic withspherical aberration corrections to produce a sharp and clear image.This depiction as simple lenses is not intended, however, to be limitingbecause it is well known that more complex lenses will produce asuperior image. Any quality of lens may nevertheless be employed in thisinvention and those skilled in the optic arts will be readily able toemploy lenses of any desired quality.

The leading linear polarizing filter 40 is located in the light pathprior to the first element of the relay lens system bracketed by 77.This is the preferred implementation because the leading linearpolarizing filter can then be used to protect the leading element of therelay lens system from visible contamination. As previously disclosed,however, the leading linear polarizing filter 40 may be located anywherein the light path prior to the passive half-wave retarder 38.

The final linear polarizing filter 41 is located anywhere in the lightpath between the new image plane represented by the dashed line 79 andthe passive half-wave retarder 38. The electric switched quarter-waveretarder is located anywhere in the light path between the leadinglinear polarizing filter 40 and the final linear polarizing filter 41.

H. Stereoscopic Producing Oculars and Ocular Adapters

The forth embodiment is a microscope ocular or ocular adapterconstructed such that when two such oculars or ocular adapters are usedin an ordinary binocular microscope head, and when the two oculars orocular adapters are rotated 180 degrees relative to each other, theyproduce a true stereoscopic image of the magnified image. Such ocularsand ocular adapters work on all lensing-objective microscopes equippedto accept at least two oculars and on any similar optical device.

FIG. 30 shows how the single objective microscope of the secondembodiment works. The passive half-wave retarder 38 at the aperture stop13 of the lens system 14, when combined with the leading linearpolarizing filter 41, causes the two halves of the aperture stop toorient the polarization of each half orthogonally to the other half. Thepolarizing beam splitter passes light of one polarization orientation tothe left ocular 74 and light of the opposite polarization orientation tothe right ocular 75. The diagram 72 shows how light passes through theaperture stop is perceived by ocular 74. The diagram 73 shows how lightpasses through the aperture stop is perceived by ocular 75.

Viewed stereopsis is caused by the perceived effect of the aperturestop's optical-encoding differing between the right and left oculars.The perceived effect of the aperture stop's optical-encoding is key.

FIG. 31 shows a non-3D binocular microscope. An unmodified objective 14and an unmodified beam splitter 34 cause identical images to beperceived by the two oculars 74 and 75. A relay lens system 77 isinterposed in the light path prior to each ocular. Recall that a relaylens system 77 can create a conjugate 15 of the original aperture stop13. By placing an optical-encoding filter 62 in each relay lens system77, and by arranging for those optical-encoding filters to beorthogonally opposed, identical perceived effects, 72 and 73, of theaperture stop's conjugate 15 are produced as were the effects of FIG. 30described above.

FIG. 32 shows diagrammatically one such implementation of a lensingarrangement for such a stereoscopic imaging ocular 14. A relay-lenssystem bracketed by 77 captures the image plane represented by thedashed line 3 produced by the microscope objective lens projectionrepresented by lines 22. The relay-lens system relays the original imageplane represented by the dashed line 3 to a new image plane representedby the dashed line 79. The new image plane represented by the dashedline 79 is viewed as an aerial image represented by 22, that is createdby ordinary ocular optics suggested by 80. Alignment is via a marker,one example of which is shown at 61 or by mechanically coupling pairstogether (not shown).

FIG. 33 shows diagrammatically one implementation of a lensingarrangement for such a stereoscopic imaging ocular adapter 14. Arelay-lens system bracketed by 77 captures the image plane representedby the dashed line 3 produced by the microscope objective lensprojection represented by lines 22. The relay-lens system relays theoriginal image plane represented by the dashed line 3 to a new imageplane represented by the dashed line 79. The adapter is equipped with asleeve 76 that allows any standard microscope ocular to be inserted whenthe diameter is the same specification.

The relay lens system shown bracketed by 77 is depicted with simplelenses for the purpose of illustration. In actual practice, such relaylens systems are composed of compound lenses that are achromatic withspherical aberration correction to produce a sharp and clear image. Thisdepiction as simple lenses is not intended, however, to be limitingbecause it is well known that more complex lenses will produce asuperior image. Any quality of lens may nevertheless be employed in thisinvention and those skilled in the optic arts will be readily be able toemploy lenses of any desired quality.

A neutral-density filter 62 placed at the created conjugate of theaperture stop 15 of the relay-lens system 77.

FIG. 34 shows the shape of the neutral-density filter 62 that is placedat the aperture stop in the ocular or ocular adapter. Theneutral-density filter is shaped to effect the transmission of lightthrough one half the aperture stop. That it effects half the aperturestop is not, however, intended to be limiting. Occluding half theaperture stop has the effect of reducing the light through that aperturestop by 50%. Any effect of more or less of a 50% occluding maynevertheless be employed in this invention and those skilled in theoptic arts will be readily be able to extend this principle to changethe shape of the edge or cut to reduce or increase the amount of lighttransmission through the aperture stop by any desirable percentage. Suchmodifications of the cut or edge include moving its position to createan occlusion of greater or less than one-half a circle.

FIG. 34 also shows that the neutral-density filter may equally well beconstructed as a hole cut through a circular plate 63. Although we showa semicircular cut, any shape hole may nevertheless be used. FIG. 34also shows that such a plate is also constructed from a cut half-disk 62coupled with a half washer 64.

FIG. 35 shows that the preferred implementation of a neutral densityfilter is to occlude the aperture stop at 100%. When the neutral densityfilter occupies half the aperture stop, a 100% blockage reduces thelight transmitted through the entire aperture stop by 50%. Someapplications may require less of a light loss. When the neutral densityfilter occupies half the aperture stop, a 50% reduction of light throughthe neutral density filter reduces the light transmitted through theentire aperture stop by 25%. When the neutral density filter occupieshalf the aperture stop and reduces light by 0%, it reduces the lighttransmitted through the entire aperture stop by 0%. A 0% occlusioneliminates the stereoscopic effect and is not recommended. That weillustrate three percentages of occlusion in FIG. 35 is not, however,intended to be limiting. Any percentage of occlusion may nevertheless beemployed in this invention and those skilled in the optic arts will bereadily be able to employ a neutral density filter of any percentage ofocclusion.

FIG. 36A shows the edge or cut 39 of the neutral-density filter 62. Thatedge or cut may be treated to minimize unwanted refractive visual noise.One implementation is to coat the edge or cut with light-absorbtivematerial, such as flat-black paint, dye, or other light absorbtiveagents. Another implementation, as shown in FIG. 36B, is to apply theneutral-density filter as a coating 65 to an optically flat transparentsurface 53, such as glass. These implementations are not intended to belimiting, however, as it is well known that edge refractions can beeliminated using a wide variety of methods. Any such method maynevertheless be employed in the invention and those skilled in the opticarts will readily be able to extend this principle to any method foreliminating undesirable edge refraction.

I. A Stereoscopic Video Lens

The fifth embodiment, as shown in FIG. 37, is a video lens systemcapable of imaging an subject 31, optical-encoding the subject's depthinformation with a leading linear polarizing filter 40, a passivehalf-wave retarder 38 at the aperture stop of the lens, an electricswitched quarter-wave retarder 48, and a final linear polarizing filter41, and recording that image on the image plane 3. The image plane 3 ofvideo camera, the body of which is represented by dashed line 55, is thefront surface of an Image Orthicon tube, a CCD array, or any other imagerecording surface. The camera is analog or digital.

The video lens system is capable of producing a sequence of images thatcan later be viewed in 3D, also called stereovision or human stereopsis.FIG. 37 illustrates such a lens system. Any of many common forms ofvideo lenses are represented by the cylinder pictured at 66. AlthoughFIG. 37 shows a fixed focal length lens, this assumption is not intendedto be limiting, however, because it is well known that lenses can beconstructed to vary their focal length, such lenses commonly beingreferred to as “zoom” lenses. Such variable focal length lenses maynevertheless be employed in the invention and those skilled in the opticarts will readily be able to extend the present principles to variablefocal length lenses.

A passive half-wave retarder 38 is placed at the aperture stop of thelens system 66. This assumption is not intended to be limiting, however,as it is well known that lens systems may have multiple effectiveaperture stops, called the aperture stop and its conjugates. Suchpositionings of the aperture stop may nevertheless be employed in theinvention and those skilled in the optic arts will readily be able toextend the present principle to any conjugate of the aperture stop. Theassumption that the aperture stop is interior to the lens system is alsonot intended to be limiting, however, because it is well known that newconjugates of the aperture stop can be constructed in the light pathprior to and/or in the light path subsequent to the an existing lenssystem. FIG. 38 shows one example of a new conjugate of an aperture stopcreated in the light path subsequent to an existing lens system 66. Atypical relay lens system, shown bracketed by 77, gathers the image atthe original image plane represented by the dashed line 3, and focuses anew image on a new image plane represented by the dashed line 79.Between the old and new image planes a new aperture stop—the position ofwhich is indicated by the dashed line 15 (a conjugate of the originalaperture stop) is created and the passive half-wave retarder 38 placedat that point. Such new conjugates of aperture stops, whether in thelight path prior to or in the light path subsequent to the lens system,may nevertheless be employed in the invention and those skilled in theoptic arts will be readily able to extend the present principle toplacement of the passive half-wave retarder in any such created externalconjugate of the aperture stop.

FIG. 37 shows that the passive half-wave retarder 38 covers one-half thearea of the aperture stop with the bisecting edge 39 oriented verticallyor near vertically. The vertical orientation is relative to normalupright orientation of the camera body, represented by the dashed line55, to which the lens system 66 is attached. This orientation is notintended to be limiting, however, as it is well known that some lenssystems rotate during use. For lens systems that rotate, the passivehalf-wave retarder 38 either attaches to a non-rotating component at theaperture stop, or is installed with hardware able to maintain thevertical orientation of its edge while the lens system rotates, or isplaced in a new external aperture stop that does not rotate with thelens system. Such positioning or hardware modifications may neverthelessbe employed in the invention and those skilled in the optic arts willreadily be able to extend the present principles to any position ormodification required to maintain a vertical orientation of thebisecting edge of the passive half-wave retarder in a rotating lenssystem.

The polarization orientation of the passive half-wave retarder 38parallels that of the polarization orientation of the leading linearpolarizing filter 40. When the leading linear polarizing filter 40 isexternal to the lens system, it adjusts to bring its polarizationorientation into parallel with the passive half-wave retarder'spolarization orientation. When both are external, one or the other orboth adjust. When both are internal to the lens system, both are fixedin the correct orientation relative to each other during manufacture.

As shown in FIG. 37, a leading linear polarizing filter 40 is interposedanywhere in the light path between the subject 31 and the passivehalf-wave retarder 38. The ideal position is external to the lens systemand optionally attached to the front of the lens system, as for examplewith a screw-on filter. Other positions are anywhere inside the lenssystem, FIG. 39A at 40, or as a coating on the front element of the lenssystem as shown in FIG. 39B at 67, that is, anywhere in the light pathprior to the passive half-wave retarder 38 in both figures.

The external position 40 of FIG. 37 is preferred because it requiresminimal modification of the lens. That position is not intended to belimiting, however, as it is well known that linear polarizing filterscan be applied as coatings to lenses and can be positioned almostanywhere inside a lens system. Any position for the linear polarizingfilter may be employed in the invention so long as it is anywhere in thelight path between the subject and the passive half-wave retarder, andthose skilled in the optic arts will readily be able to extend thisprinciple to any acceptable position inside or outside of the lenssystem.

The polarization orientation of the leading linear polarizing filter 40in FIG. 37 must be parallel to the polarization orientation of theelectric switched quarter-wave retarder 48 when the electric switchedquarter-wave retarder is powered and is in one or the other of its twoplus or minus 45° positions. When the leading linear polarizing filter40 is in the light path prior to the lens system it is manuallyadjustable for alignment. When the linear polarizing filter is internalto the lens system as with 40 in FIG. 39A, or is applied to a lens as 67in FIG. 39B, adjustment is made by altering the position of the electricswitched quarter-wave retarder. When the electric switched quarter-waveretarder is also inside the lens system 48 in FIG. 40A, adjustment ismanufactured into all components of the lens system. The means oforientation is not intended to be limiting, however, as it is well knownthat a linear polarizing filter can be oriented using any of a number ofwell known methods. Any such method may nevertheless be employed in theinvention and those skilled in the optic arts will readily be able toextend this principle to any method of orientation.

As shown in FIG. 37, an electric switched quarter-wave retarder 48 isplaced anywhere in the light path between the leading linear polarizingfilter 40 and the final linear polarizing filter 41. Position 48 is thepreferred implementation because it requires a component of minimalexpense (smaller size). FIGS. 40A, 40B, 40C, and 40D show otheracceptable positions. The electric switched quarter-wave retarder may bepositioned anywhere in the optical path between the leading linearpolarizing filter 40, and the final linear polarizing filter 41. Theposition of the electric switched quarter-wave retarder is irrespectiveof the position of the passive half-wave retarder 38. The electricswitched quarter-wave retarder can be placed inside the lens and in thelight path subsequent to the passive half-wave retarder 38, as in FIG.40A at 48, or inside the lens and in the light path prior to the passivehalf-wave retarder 38, as in FIG. 40B at 48, or in the light path priorto the lens and in the light path subsequent to the leading linearpolarizing filter 40, as in FIG. 40C at 48, or in the light pathsubsequent to the lens and in the light path prior to the final linearpolarizing filter 41, as in FIG. 40D at 48.

In FIG. 37, the orientation of the electric switched quarter-waveretarder 48 parallels that of the leading linear polarizing filter 40.The two parallel each other when the electric switched quarter-waveretarder is in one or the other of its electrically energizedorientations. When the electric switched quarter-wave retarder isinstalled in an external housing prior to the lens system as at 48 ofFIG. 40C it may or may not be made adjustable. When the electricswitched quarter-wave retarder is installed inside the lens system, asat 48 of FIG. 40B or FIG. 40A, the leading linear polarizing filter isadjustable when external at 40. When both the electric switchedquarter-wave retarder is internal, and the linear polarizing filter isfixed, the lens systems may be manufactured in permanent correctalignment. When the electric switched quarter-wave retarder is insidethe camera body, it is adjustable when the camera body allows, otherwiseit is non-adjustable. When the electric switched quarter-wave retarderis non-adjustable, then either the leading linear polarizing filter isadjustable, or the lens system is manufactured to permanently align withthe fixed electric switched quarter-wave retarder.

The electric switched quarter-wave retarder requires two differentvoltage potentials to set it into one or the other of its polarizingeffecting orientations. When the electric switched quarter-wave retarderis internal, as at 48 of FIG. 40A or FIG. 40B, energy is supplied eithervia a corresponding external cable 49 or via electrical contacts 68 inthe lens system's housing. When the electric switched quarter-waveretarder is external, FIG. 40C or FIG. 40D, energy is supplied viaexternal wires 49. As shown in FIG. 41, when the electric switchedquarter-wave retarder 48 is inside the camera body 55, energy isprovided via the internal camera body wires 49.

In FIG. 37, the final linear polarizing filter 41 is placed anywhere inthe light path between the passive half-wave retarder 38 and the imageplane 3. The preferred implementation is outside the lens system at 41and in proximity to the electric switched quarter-wave retarder 48,because this placement allows the lens system to be used for otherpurposes when not being dedicated to stereovision use. Other locationsfor the final linear polarizing filter are shown in FIGS. 42A and 42B.The final linear polarizing filter, when inside the lens system 66, mustbe in the light path subsequent to the passive half-wave retarder 38, asat 41 in FIG. 42A; when the final linear polarizing filter is inside thecamera body 55, it must be in the light path prior to the image plane 3,as at 41 in FIG. 42B.

As in FIG. 37, the final linear polarizing filter 41 has itspolarization orientation oriented in parallel with the polarizationorientation of the leading linear polarizing filter 40. When the finallinear polarizing filter outside the lens system as at 41, it may beadjustable to achieve proper orientation. When the final linearpolarizing filter is inside the lens system, as in FIG. 42A, or insidethe camera body, as in FIG. 42B, the final linear polarizing filter maybe internally adjustable, or may be manufactured to be in the correctalignment.

J. A Generic Video Adapter

The sixth embodiment, as shown diagrammatically in FIG. 43, is a videolens adapter capable of enabling a wide variety of video lenses andcameras to produce stereographic images. This adapter works with anylens that can be mounted at mount point 69. This adapter works with anyvideo camera that will accept the adapter's mounting hardware 70. Theadapter captures the lens output image as represented by lines 22, andrelays that image from the original image plane represented by thedashed line 3 to the video camera's new image plane represented by thedashed line 79. The image plane represented by the dashed line 79 of thevideo camera 55 is the front surface of an Image Orthicon tube, a CCDarray, or any other image recording surface. The video camera is digitalor analog.

The video lens adapter is capable of producing a sequence of images thatcan later be viewed in 3D, also called stereovision or human stereopsis.FIG. 43 illustrates diagrammatically such an adapter.

The adapter is designed to allow a lens to be mounted at the adapter'sfront end 69, and to allow the adapter to be mounted to a camera body,at 70. The preferred implementation is that the front and rear mounts befemale and male C-mounts respectively. This preference is not, however,intended to be limiting, because it is well known there are manydifferent standards for lens mounts. Canon, for example, uses EOS mountsfor most of its cameras, and many industrial lenses and cameras useT-mounts. Such other mounts may nevertheless be used in conjunction withthis adapter, either at the front as a lens mount, or at the rear as acamera mount, or both, and those skilled in the mechanical arts will bereadily able to extend the present principle to any suitable lens mount.

A relay lens system, bracketed by 77, inside the adapter, gathers theimage 22 from the attached lens that normally focuses at the originalimage plane represented by the dashed line 3, and relays that image to anew image plane represented by the dashed line 79 inside the camera. Therelay lens system as depicted is not, however, intended to be limiting,because optical theory allows relays lens systems to be constructed in avariety of ways. The only requirements for the relay lens system arethat it create a conjugate of the lenses aperture stop—the position ofwhich is indicated by the dashed line 15, and that it copy unaltered theoriginal image plane represented by the dashed line 3 to the new imageplane represented by the dashed line 79. Any suitable relay lens systemmay nevertheless be employed in the invention and those skilled in theoptic arts will be readily able to extend the present principle to anyrelay lens system that satisfies the two requirements.

The relay lens system shown bracketed by 77 is depicted with simplelenses for the purpose of illustration. In actual practice, such relaylens systems are composed of compound lenses that are achromatic withspherical aberrations corrected to produce a sharp and clear image. Thisdepiction as with simple lenses is not intended, however, to be limitingbecause it is well known that more complex lenses will produce asuperior image. Any quality of lens may nevertheless be employed in thisinvention and those skilled in the optic arts will be readily be able toemploy lenses of any desired quality.

A passive half-wave retarder 38 is placed at the conjugate of the lensaperture stop that is created by the adapter—the position of which isindicated by the dashed line 15.

FIG. 44 is an exploded view of the adapter. It shows that the passivehalf-wave retarder 38 covers one-half the area of the aperture stop withthe bisecting edge 39 oriented vertically or near vertically. Thevertical orientation is relative to normal upright orientation of thecamera to which the adapter is attached.

As shown in FIG. 44, a leading linear polarizing filter 40 is interposedin the light path between the lens mounted at 69 and the passivehalf-wave retarder 38. The ideal position is between the lens mountinghole at 69 and the front element of the relay lens system 71. Thisposition allows the front linear polarizing filter to protect the frontsurface of the front relay lens element from contaminants. Anotherposition that is desirable is inside the lens mounting 69. In thatposition the front analyzing polarizer servers as a seal for the adapteras a whole, a desirable characteristic for medical use. Any position forthe front linear polarizing filter may be employed in the invention solong as it is between the lens mounting hole and the passive half-waveretarder, and those skilled in the optic arts will readily be able toextend this principle to any acceptable position.

The polarization orientation of the leading linear polarizing filter 40must be parallel to the polarization orientation of the electricswitched quarter-wave retarder 48 when the electric switchedquarter-wave retarder is powered and is in one of its two plus or minus45° positions.

As shown in FIG. 44, an electric switched quarter-wave retarder 48 isplaced anywhere in the light path between the leading linear polarizingfilter 40 and the final linear polarizing filter 41. Position 48 is thepreferred implementation because it requires a component of minimalexpense (smaller size). FIGS. 40B and 40C show that the electricswitched quarter-wave retarder works equally well in the light pathprior to the passive half-wave retarder. In FIG. 44, the electricswitched quarter-wave retarder 48 may be positioned anywhere in theoptical path between the leading linear polarizing filter 40, and thefinal linear polarizing filter 41. The position of the electric switchedquarter-wave retarder is irrespective of the position of the passivehalf-wave retarder 38.

The orientation of the electric switched quarter-wave retarder 48parallels that of the leading linear polarizing filter 40. The twoparallel each other when the electric switched quarter-wave retarder isin one or the other of its electrically energized orientations.

As shown in FIG. 44, the final linear polarizing filter 41 is placedanywhere in the light path between the passive half-wave retarder 38 andthe camera mount point 70. The preferred implementation is near to orinside the camera mount 70. When inside the camera mount, the finallinear polarizing filter acts to seal the adapter from contaminants, asfor medical use.

The final linear polarizing filter 41 has its polarization orientationoriented in parallel with the polarization orientation of the leadinglinear polarizing filter 40.

K. A Stereographic Light-Valve

The seventh embodiment, as shown diagrammatically in FIG. 45, is astereographic light-valve capable of insertion into to aperture stop, orthe conjugate of the aperture stop, of any imaging lens system to enablethat lens system to produce stereographic video or motion picture imagesequences. This stereographic light-valve can be retrofitted intoexisting lens system and can be manufactured into new lens system.Examples of such lens systems include microscope objectives, endoscopes,video lenses, and motion picture lenses. Although these examples are theonly ones cited, they are not intended to be limiting. Any imaging lenscan be used to exploit this stereographic light-valve and suchunforeseen applications are considered a part of this embodiment.

The stereographic light-valve is capable of producing a sequence ofimages that can later be viewed in 3D, also called stereovision or humanstereopsis. FIG. 45 illustrates diagrammatically such a stereographiclight-valve.

The stereographic light-valve is a sandwich made of four components. Aleading linear polarizing filter 40 is first in the light path. A finallinear polarizing filter 41 is last in the light path. Between the twois a passive half-wave retarder 38 and an electric switched quarter-waveretarder 48. The linear polarizing filters 40 and 41 must be first andlast in the light path. The passive half-wave retarder 38 and anelectric switched quarter-wave retarder 48 can appear in the order shownor in the reverse order with no difference in function.

The stereographic light-valve is constructed as thin as possible toavoid space conflict with any lens elements that surround the aperturestop. In the event that materials prevent a sufficiently thin constructsuch that the entire stereographic light-valve occupies only the spaceof the aperture stop, the stereographic light-valve is placed such thatthe passive component, the passive half-wave retarder, is precisely atthe aperture stop, or one of the aperture stop's conjugates.

FIG. 46 is an exploded view of the stereographic light-valve. It showsthat the passive half-wave retarder 38 covers one-half the area of theaperture stop with the bisecting edge 39 oriented vertically or nearvertically. The vertical orientation is relative to normal uprightorientation of the lens into which the adapter is installed.

The polarization orientation of the leading linear polarizing filter 40must be parallel to the polarization orientation of the electricswitched quarter-wave retarder 48 when the electric switchedquarter-wave retarder is powered and is in one of its two plus or minus45° positions.

The final linear polarizing filter 41 has its polarization orientationoriented in parallel with the polarization orientation of the leadinglinear polarizing filter 40.

FIG. 47 shows that the stereographic light-valve can be construct fromcoatings on the electric switched quarter-wave retarder 48. Aquarter-wave retarder 38 is first coated to one half of one of theelectric switched quarter-wave retarder's faces. Two equally alignedlinear polarizing filters are then coated to both sides of the faces ofthe electric switched quarter-wave retarder, the leading linearpolarizing filter 40 to one face, and the trailing linear polarizingfilter 41 to the other face.

I claim:
 1. A method for processing a light beam, comprising: (a)passing the light beam through a leading polarizing filter to form afiltered light beam such that at least most of the light in the filteredlight beam has a common polarization orientation; (b) passing a firstportion and not a second portion of the filtered light beam through aretarder to provide the first portion of the filtered light beam havinga first polarization orientation and the second portion having a secondpolarization orientation different from the first polarizationorientation, the retarder being positioned at least substantially at theaperture stop or a conjugate thereof; and (c) passing the first andsecond light portions through one or more analyzing filters, wherein theone or more analyzing filters is a polarizing beam splitter.
 2. Themethod of claim 1, wherein the retarder has a polarization orientationthat is at least substantially parallel to the polarization orientationof the leading polarizing filter.
 3. The method of claim 1, wherein thepassing step (c) includes: spatially separating the first and secondlight portions based on the first and second polarization orientations,respectively.
 4. The method of claim 1, further comprising an electricswitched retarder positioned in the optical path of the light beam,filtered light beam, or first or second light portions.
 5. The method ofclaim 1, wherein the retarder covers only a portion of the aperture stopor conjugate thereof.
 6. The method of claim 1, wherein the first andsecond light portions follow a common optical path before contacting thepolarizing beam splitter and separate optical paths after passingthrough the polarizing beam splitter.
 7. The method of claim 1, wherein,in the passing step (b), the filtered light beam converges on an imageplane.
 8. The method of claim 1, wherein the one or more polarizingfilters are located in an objective lens.
 9. The method of claim 1,wherein the retarder is located in an objective lens.
 10. The method ofclaim 1, wherein the light beam, in passing step (a), passes through asingle aperture.
 11. The method of claim 1, wherein the light beam, inpassing step (a), follows a single optical path.
 12. The method of claim1, wherein the light beam in passing step (a) and the first and secondportions in passing step (b) correspond to a common optical channel.